The present invention relates to hand-held medical diagnostic instruments of the type which contain a light source, and is more particularly concerned with a streak retinoscope in which a bar or streak of light can be focussed and defocussed and continuously adjusted at any angle by use of a control sleeve on the instrument's handle.
Streak retinoscopy provides the eye practitioner with valuable information about the refractive state of a patient's eyes. Streak retinoscopy, in conjunction with trial lenses, can not only measure the refractive error of the eye but can also determine the axis of astigmatism.
In streak retinoscopy, a streak or bar of light, as distinguished from a spot of light, is projected through the lens of the eye onto the retina, and the image of the streak on the retina is observed by the practitioner. For effective examination, the streak or bar should be fully rotatable 360 degrees and beyond without a stop. Full 360 degree rotation is advantageous in that the streak can be rotated from any starting position. The physician or other practitioner should also be afforded freedom in the use of hands, so that the angular and focussing adjustments can be carried out with the right hand alone or with the left hand alone.
A typical retinoscope illustrative of the state of the art is shown and described in U.S. Pat. No. 3,439,978, granted Apr. 22, 1969, and is also shown in U.S. Pat No. Des. 243,973, granted Apr. 5, 1977.
Other hand-held diagnostic instruments having a light source and a power source contained in their handles are shown in U.S. Pat. No. 4,147,163, granted Apr. 3, 1979, and in U.S. Pat. No. 3,441,340, granted Apr. 29, 1969.
The present retinoscopes as described e.g. in U.S. Pat. No. 3,439,978 usually achieve rotation with a control sleeve that is fitted inside an outer sleeve. The outer sleeve has openings or slots that permit the practitioner to rotate the control sleeve using his or her fingers. The control sleeve can also be manipulated up and down within the outer sleeve to move the lens nearer or further from the lamp.
The retinoscope of this system requires adjustment of the angular position of the head to the handle for convenient positioning of the slots in the outer sleeve. This can require loosening and tightening of a separate nut or actually removing the head and adjusting the orientation of the head to slots. Some instruments do not allow adjustment of slot orientation to head. Some retinoscopes have external control sleeves but because of mechanical constraints cannot rotate more than about 180 degrees.